-- |Utilities for working with fragment and vertex shader programs.
module Graphics.GLUtil.Shaders (loadShader,
                                linkShaderProgram, linkShaderProgramWith,
                                namedUniform, 
                                uniformScalar, uniformVec, uniformMat, 
                                namedUniformMat, uniformGLMat4) where
import Control.Monad (unless)
import qualified Data.ByteString as BS
import Graphics.Rendering.OpenGL
import Graphics.Rendering.OpenGL.Raw.Core31
import Graphics.GLUtil.GLError
import Foreign.Ptr (Ptr)
import Unsafe.Coerce (unsafeCoerce)

-- 'loadShader' is based on the ogl2brick example in the GLUT package.

-- |Load a shader program from a file.
loadShader :: ShaderType -> FilePath -> IO Shader
loadShader st filePath = do
  shader <- createShader st
  BS.readFile filePath >>= (shaderSourceBS shader $=)
  compileShader shader
  printError
  ok <- get (compileStatus shader)
  infoLog <- get (shaderInfoLog shader)
  unless (null infoLog)
         (mapM_ putStrLn 
                ["Shader info log for '" ++ filePath ++ "':", infoLog, ""])
  unless ok $ do
    deleteObjectNames [shader]
    ioError (userError "shader compilation failed")
  return shader

-- |Link shaders into a 'Program'.
linkShaderProgram :: [Shader] -> IO Program
linkShaderProgram shaders = linkShaderProgramWith shaders (const $ return ())

-- |Link shaders into a 'Program' with the given action performed
-- after attaching shaders, but before linking the program. This is
-- most commonly used to set the 'bindFragDataLocation' state
-- variable.
linkShaderProgramWith :: [Shader] -> (Program -> IO ()) -> IO Program
linkShaderProgramWith shaders prelink = do p <- createProgram
                                           mapM_ (attachShader p) shaders
                                           prelink p
                                           linkProgram p
                                           return p

-- |Work with a named uniform shader parameter. Note that this looks
-- up the variable name on each access, so uniform parameters that
-- will be accessed frequently should instead be resolved to a
-- 'UniformLocation'.
namedUniform :: Uniform a => String -> StateVar a
namedUniform name = makeStateVar (loc >>= get) (\x -> loc >>= ($= x))
  where loc = do Just p <- get currentProgram
                 l <- get (uniformLocation p name)
                 printError
                 return $ uniform l

-- Allocate an OpenGL matrix from a nested list matrix, and pass a
-- pointer to that matrix to an 'IO' action.
withHMatrix :: [[GLfloat]] -> (Ptr GLfloat -> IO a) -> IO a
withHMatrix lstMat m = do
    mat <- newMatrix RowMajor (concat lstMat) :: IO (GLmatrix GLfloat)
    withMatrix mat (\_ -> m)

-- Not all raw uniform setters are wrapped by the OpenGL interface,
-- but the UniformLocation newtype is still helpful for type
-- discipline.
unUL :: UniformLocation -> GLint
unUL = unsafeCoerce

-- |Set a 'UniformLocation' to a scalar value.
uniformScalar :: UniformComponent a => UniformLocation -> SettableStateVar a
uniformScalar loc = makeSettableStateVar $ (uniform loc $=) . Index1

-- |Set a 'UniformLocation' from a list representation of a
-- low-dimensional vector of 'GLfloat's. Only 2, 3, and 4 dimensional
-- vectors are supported.
uniformVec :: UniformLocation -> SettableStateVar [GLfloat]
uniformVec loc = makeSettableStateVar aux
  where aux [x,y] = glUniform2f loc' x y
        aux [x,y,z] = glUniform3f loc' x y z
        aux [x,y,z,w] = glUniform4f loc' x y z w
        aux _ = ioError . userError $
                "Only 2, 3, and 4 dimensional vectors are supported"
        loc' = unUL loc

-- |Set a named uniform shader parameter from a nested list matrix
-- representation. Only 3x3 and 4x4 matrices are supported.
namedUniformMat :: String -> SettableStateVar [[GLfloat]]
namedUniformMat var = makeSettableStateVar (\m -> loc >>= ($= m) . uniformMat)
  where loc = do Just p <- get currentProgram
                 location <- get (uniformLocation p var)
                 printError
                 return location

-- |Set a uniform shader location from a nested list matrix
-- representation. Only 3x3 and 4x4 matrices are supported.
uniformMat :: UniformLocation -> SettableStateVar [[GLfloat]]
uniformMat loc = makeSettableStateVar aux
  where aux mat = do withHMatrix mat $ \ptr ->
                       case length mat of
                         4 -> glUniformMatrix4fv loc' 1 1 ptr
                         3 -> glUniformMatrix3fv loc' 1 1 ptr
                         _ -> ioError . userError $ 
                              "Only 3x3 and 4x4 matrices are supported"
        loc' = unUL loc

-- |Set a uniform shader location with a 4x4 'GLmatrix'.
uniformGLMat4 :: UniformLocation -> SettableStateVar (GLmatrix GLfloat)
uniformGLMat4 loc = makeSettableStateVar aux
  where aux m = withMatrix m $ \_ -> glUniformMatrix4fv loc' 1 1
        loc' = unUL loc